Traditional high speed computer and communications systems are often built using a backplane assembly. Such systems are built on several printed circuit boards (“PCB”), called “daughter boards” or “daughter cards”, that are interconnected through a backplane.
A traditional backplane is a printed circuit board that has many signal traces running through it. The traces route signals between electrical connectors mounted on a surface of the backplane. The daughter cards have mating electrical connectors along one edge, allowing each daughter card to be plugged into the backplane. In this configuration, the daughter cards are parallel to each other and mounted typically at right angles to the backplane.
As the need for bandwidth in our technological society has increased, it is evident that existing communications systems will not have the capacity to provide the desired bandwidth. Thus, high-speed systems must be developed which use light to transmit data signals, in addition to the existing electrical communication architecture. Data can then be transmitted at very high rates (e.g., 10 gigabits per second). Instead of metal traces, such systems use optical fiber or waveguides to transmit the light.
It should be realized that optical communications is not like electronic communications. Light is an electromagnetic radiation having unique characteristics that are different from the characteristics of electrons. Therefore, designing a backplane assembly for light transmission has different considerations from designing a backplane assembly for electronic transmission.
A backplane assembly designed for light transmission generally includes connectors that have a ferrule holding a single optical fiber or a multi-fiber optical ribbon. The ferrule on the daughter card connector is mated with a corresponding ferrule on the backplane connector so that the optical fibers held in the mating ferrules are aligned to minimize loss. These ferrules are conventionally placed in the mating position by alignment pins and passages for receiving the alignment pins.
Due to the size of the optical fibers utilized, for example 125 micron (10−6 meter) diameter with a 62.5 micron diameter core, it is critical to maintain precise tolerances with the alignment pins and the receiving passages. Failure to maintain precise tolerances and any other misalignment/defect could lead to significant loss of data signals at the fiber-to-fiber interface.
As more and more backplane assemblies incorporate both electrical connectors and fiber optic connectors, the above alignment/tolerance problems are further complicated by the need for the backplane assembly to accommodate variable wipe length. As used herein, “wipe length” refers to the distance required for the electrical connectors on the daughter card and backplane to establish electrical engagement. Typically, the electrical connectors are mounted on the edge of the daughter card often near the optical connectors.
This “wipe” is required primarily to counteract accumulated tolerances within the backplane/daughter card enclosure. Factors such as PCB uniformity, planarity, positional tolerancing, PCB lock location, component tolerancing and connector binding, all play roles in the final position of the electrical connectors in relation to the PCBs. These same factors can be detrimental to fiber optic connectors.
Fiber optic connectors function as butt-coupled devices. The end faces holding the optical fibers must remain in physical contact at all times to ensure that the optical signals traveling in the optical fibers are stable and uninterrupted. Therefore, fiber optic connectors must be designed to establish full engagement and provide “float” (movability in the axis of engagement) to accommodate the variable wipe of the electrical connectors. There are two main reasons for this.
First, mating forces in excess of 150 lbs. can be generated when joining high-density electrical connectors. Manual cam latch mechanisms are conventionally used to join the individual daughter cards to the backplane. These mechanisms, although manually operated, do not provide much user feedback other than a go or no-go type situation. With this being the case, if any connector is not properly aligned under such loads, then there is a strong likelihood of problems for the connection system. Therefore, it is critical that individual connectors are aligned before the latches are engaged. Furthermore, it is desirable to isolate mating force spikes by staggering the mating sequence from optical to electrical. This will provide for smoother cam latch activation when attempting to seat the daughter card on the backplane. Also, any additional loads that could bring the latches beyond their elastic limit are removed.
Second, in order to accommodate different electrical connectors and to have a product that is easily leveraged into new technologies, it is important to maximize the float to ensure compatibility and limit the possibility of conjoined future force spikes. For these characteristics to be provided, reasonably large Z-axis travel (here, the Z-axis has been selected as the axis of engagement), for example on the order of 3 to 7 millimeters, is desired. This requires that the fiber optic connectors and the electrical connectors move in relation to one another; otherwise, components would be damaged or destroyed under the force of lever arms for engaging daughter cards to the backplane.
To achieve the desired float, a slidable mechanism is typically employed within the system. For example, a prior art system disclosed in U.S. Pat. No. 5,121,454 issued to Iwano et al. utilizes side latches incorporated into the connector housing for mating, and the configuration of the latches and the connector housing provide float in the Z-direction. The latching approach of the prior art '454 patent is described in more detail with respect to FIG. 1 in the Detailed Description section.
The inventors of the present invention have recognized that while prior art fiber optic connection systems function adequately for the most part, there are disadvantages that have not been addressed by the prior art systems. First, the prior art systems known to the inventors do not provide design flexibility. For example, as the number of optical fibers or other requirements in a connector changes, there is a need to retool and redefine the design to satisfy such requirements. And this retooling/redefinition process is costly and time consuming. Referring back to the fiber optic connector disclosed in the prior art '454 patent, it is apparent to one of ordinary skill in the art that should the connector requirements change (e.g., requiring more optical fibers to be held by the connector), the connector design will have to be redefined and substantial retooling will be necessary.
Second, because of the substantial mating forces present, the prior art systems employ complex latch/release mechanisms which tend to increase the size and material cost of the connection system. More importantly, perhaps, this increased size of the connection system occupies valuable space on the printed circuit board—which space could have been utilized by other components.
What is desired, therefore, is a fiber optic connection system that addresses these disadvantages of prior art systems by providing for design flexibility in a cost-effective, time saving manner.